The invention has been conceived particularly, though not exclusively, as an aid for use in executing shipboard rolling vertical landings. The so-called rolling vertical landing (RVL) is a type of landing executed by vectored-thrust vertical/short takeoff and landing (V/STOL) and short takeoff and vertical landing (STOVL) aircraft as an alternative to a normal vertical landing, in which the aircraft approaches at an angle to the ground and at relatively slow speed (in comparison to conventional fixed-wing landings) under a combination of jet-borne and wing-borne lift. Aircraft of this class include the well known V/STOL Harrier and Sea Harrier “jump jet” variants, and the STOVL F-35B variant of the Lightning II yet to enter service. The RVL was developed originally as a manoeuvre for landing on unprepared areas in land-based operations so that debris disturbed by the jet efflux would tend to be blown behind the aircraft and not into the engine intakes. It is also considered to be a useful technique for shipboard operations, however, due to the ability to land with a higher aircraft weight than would be possible in the same meteorological conditions if a vertical landing was to be used, or to land at the same weight but with a reduced power setting as compared to the vertical landing thereby potentially increasing engine life. Other benefits can include a reduction in the erosion of deck coverings by engine exhaust as compared to vertical landings. While conceived with shipboard RVLs by V/STOL and STOVL aircraft in mind, however, the present invention may also find application as an aid for conventional (wire-arrested) fixed wing carrier-borne landings which are typically conducted with shallower approach angles and at substantially higher speeds than RVLs, and also for helicopter landings if not performed vertically.
Note: all references in this specification to landing directions, approach angles, glideslopes etc. in the context of landings on vessels which may be underway are to those directions, angles, glideslopes etc. relative to the overall moving platform and not to the actual movement of the aircraft through the air.
A VLA currently in service with some navies for conventional fixed wing carrier-borne landings is the so-called Improved Fresnel Lens Optical Landing System (IFLOLS). This comprises a set of lights located on the deck offset laterally from the runway and directed towards approaching aircraft. There is a horizontal row of datum lights to either side of a central vertical column of indicator lights which are selectively lit so that at any time the position of the illuminated indicator light (known as the “ball”) relative to the datum lights indicates to the pilot whether he is above, below or upon a specified glideslope. This can be stabilised for pitch, roll and heave of the deck with the apparatus being tilted on gimbals as required to maintain its indication of the correct glideslope. It requires the pilot to scan laterally away from the runway centreline to use the aid, however, and significant training is required in order to prevent pilots from inadvertently reacting instead to deck motion, known as “deck spotting”. It is also expensive to maintain due to the number of moving parts, and occupies useful deck space.